I know it difficult to believe, but—people cheat—and they cheat at breaking. Losers as well as "Masters" have been known to cheat at breaking; not so much at tournaments, but definitely at demonstrations.
Baking wood to dry it is cheating. Green, high moisture wood is pliable and very difficult to break. Dry wood is relatively easy to break. Try to break a green twig and then try to break a dried twig, which is easier to break?
Holding bricks up above the support for breaking is cheating since you are actually slamming the upheld end into the support block.
Sawing part way through a ice block with a string and then letting the cut refreeze is cheating.
Soaking cinder blocks in acetone to break down the concrete bond is cheating. Soaking limestone rocks will make them softer.
Spraying WD-40 or other light oil on the teeth of plastic boards will make them easier to break. Warming the boards will make the plastic softer and easier to break. Using thin rebreakable boards that have special clips that make a loud snap when they are broken.
Using spacers between the boards or blocks, while not actually cheating since the spacer are visible, is deceiving. For example, with spacers, you are not breaking 1 six inch thick board with one strike, you are breaking 6 one inch boards, one at a time with the one strike, Without spacers, since you are breaking what is essentially one thick piece of material, you use a technique with a very powerful, short, snapping motion. With spacers, since you are breaking many thin pieces of material one at a time, you use a technique with a less powerful force applied over a longer distance so you can penetrate all the boards. If two boards are placed very tightly against each other, then they will behave much as a single board with twice the thickness, with eight times the moment of elastic inertia. Therefore, the break will be not two, but eight times more difficult to break!